The invention relates to a dry-shaving apparatus which comprises a housing, an electric drive motor in the housing, one or more stationary external cutting members which project from the housing and which are provided with hair entrance apertures there are a corresponding number of internal cutting members which are covered by the external cutting members and which co-operate therewith internally, comprising a multiplicity of shaving cutters with cutting edges, and a corresponding number of drive studs which are coupled to the internal cutting members and are rotatable by the motor for driving the internal cutting members in a rotary fashion; also there are hair-pulling members associated with the shaving cutters, which are disposed at the front viewed in the direction of rotation of the cutters.
Shaving apparatus of this thype are known from U.S. Pat. No. 3,088,205, wherein the cutters, viewed in the direction of movement, are either preceded by hair-pulling members which consist of thin flexible metal sheet, which are arranged parallel to the shaving cutters, or by hair-pulling members which engage with the shaving cutters, and take the form of strips of an elastic material such as a soft rubber. The hair pulling members are slightly shorter than the shaving cutters. The shaving cutters are in contact with the underside of the stationary shear plate with the side of their cutting edges, while the hair-pulling members only extend up to a short distance thereof and are consequently not in contact with the stationary cutter.
The U.S. Pat. No. 3,088,205 discloses one of the attempts to design a shaving apparatus which is capable of shaving off the face hairs not only down to skin level, but even down to a level below that of the skin. In order to achieve this the individual hairs to be shaved off must be slightly pulled up from the skin before being shaved off. After being shaved off, the hair is released and will retract into the skin owing to the natural elasticity of the tissue which surrounds the hair. By shaving off the hair at skin level at the instant that it is pulled up from the skin, it is achieved that after the hair has been shaved and has withdrawn into the skin said hair is located below the skin surface.
The shaving appliances known from the cited U.S. Patent aim at an action which, briefly summarized, amounts to the fact that the hair pulling member presses a hair which penetrates through the hair entrance aperture of the stationary cutter against the edge of the hair entrance aperture, folds it and pulls it slightly upwards from the skin owing to friction. If this construction is to have the required effect, the hairs to be cut must be comparatively long, flexible and also soft. However, investigstions have revealed that in practice these requirements are not met. The normal 1-day beard exhibits stubbles of a length which is only a few times, namely three to four times the hair thickness. Consequently, such stubbles are comparatively short and also stiff owing to their low length- diameter ratio. They are also comparatively hard, certainly from a dynamic point of view, i.e. in relation to the speed with which they are shaved off, so that as they are cut off they exert a substantial force component on the cutter in the direction perpendicular to the cutting plane. This force component tends to push the cutter away from the stationary shear plate and increases according as the hair is disposed more obliquely in the direction of movement of the cutter. Thus, sharply bent hairs tend to push the internal cutting member away from the external cutting member. Unless the internal cutting member is pressed against the external cutting member with a disproportionately great force, there will be play between the two cooperating cutting members. As a result, a reduced cutting action is obtained and the beard stubbles are cut off in a jagged manner, more or less in their longitudinal direction.
The situation is influenced by the wear of the internal cutting member. Owing to wear, the distance from the end of the hair pulling member to the inner side of the external cutting member changes. This distance may even be reduced to nil, so that the hair pulling member may also get into the hair entrance apertures of the external shaving member, especially when it consists of a soft rubber.